Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: December 15, 2010
Publication Date: August 1, 2011
Citation: Flanagan, D.C. 2011. Application of the WEPP model to hillslopes and small watersheds in the US. In: Shukla, M.K., editor. Soil Hydrology, Land Use and Agriculture: Measurement and Modelling. Wallingford, UK: CABI. 5:137-150. Technical Abstract: Soil erosion continues to be the largest threat to maintaining sustainable agricultural production. Detachment and removal of soil and sediment by the erosive forces of wind and water degrades on-site soil quality, as well as off-site water quality and air quality. Erosion removes the upper layers of soils, which are often those that have the greatest organic matter content, and nutrient- and water-holding capacities. Cultivated and eroded soils often have reduced aggregate stability and a propensity to seal at the surface, reducing water and air intake into the plant root zone, and increasing runoff and associated erosion. Runoff water, as well as sediment particles transported in that water, usually contain agricultural chemicals – nutrients (nitrogen (N), phosphorus (P), and others) and pesticides, which can impact downstream water bodies and drinking water supplies. Problems such as silting in of rivers and harbors, eutrophication in the Great Lakes, and hypoxia in the Gulf of Mexico are largely related to surface and subsurface runoff, sediment losses, and chemical losses from high-input and high-productivity agricultural systems. Sediment remains the largest pollutant of water by volume, and results in billions of dollars in dredging costs each year to maintain drainage and navigability in rivers and other water bodies. Soil erosion caused by water (raindrop impact, overland water flow, channel erosion, gully erosion) is globally the largest erosion problem on agricultural lands, though in some climatic regions erosion due to wind detachment and transport is the greater concern. Managing agricultural lands to control and minimize soil erosion is an important mission, which is carried out by landowners, farmers, and federal, state, and local conservation agency personnel. With increasing concerns related to runoff and off-site sediment losses, new process-based technology has been developed by the United States Department of Agriculture (USDA) to provide additional information on land management impacts on not only soil erosion, but also runoff from hillslope profiles as well as small watersheds. The Water Erosion Prediction Project (WEPP) was initiated in 1985, and currently provides modeling capabilities to assess spatial and temporal soil loss, impacts of various land management, and soil conservation practice implementation on runoff, erosion, and sediment delivery from slope profiles as small as a few square meters up to small watersheds several hundred hectares in size. This chapter will provide information on the WEPP model background, physical processes simulated, available user interfaces, and applications of the model for a variety of hillslope and watershed situations. Some novel uses of WEPP will also be presented and discussed.